Theoretically, it'll be the same but mod_gzip allows more tweaking (in terms of compression); this module does not (if it uses Compress::Zlib's default gzip mechanism, compression is set at 4 iirc; 1 would be best for speed purposes and CPU load).
Anyways, if you already have mod_gzip on your server and it's compressing CGI output, don't bother to install this hack; it'll just waste CPU clicks.
Donate to UBBDev today to help aid in Operational, Server and Script Maintenance, and Development costs.
Please also see our parent organization VNC Web Services if you're in the need of a new UBB.threads Install or Upgrade, Site/Server Migrations, or Security and Coding Services.